Project Sanguine

The initially proposed system, hardened to survive a nuclear attack, would have required a giant antenna covering two-fifths of the state of Wisconsin.

At ELF frequencies, the bandwidth of the transmission was very small, so the system could only send short-coded text messages at a very low data rate.

These signals were used to summon specific vessels to the surface to receive longer operational orders by ordinary radio or satellite communication.

[2] The project was controversial from the start and was attacked by politicians, antiwar and environmental groups concerned about the effects of high ground currents and electromagnetic fields on the environment.

[1][2][3] The system became nominally operational in 1989, 20 years after it first went online as "test facility," and was used until 2004, when the US Navy declared it obsolete and it was shut down and dismantled.

The system transmitted continuously, 24 hours a day, sending an "idle" message when it was not being used so that submarines could verify they were within communication range.

[7] Submarines are shielded by seawater from all ordinary radio signals and, therefore, are cut off from communication with military command authorities while submerged.

To receive VLF signals, subs must rise to just under the surface or trail a shallow antenna buoy, making them vulnerable to detection by the enemy.

ELF transmitters use huge antennas called ground dipoles consisting of tens to hundreds of kilometers of overhead cables resembling ordinary power transmission lines.

This weak signal reached submarines over half the globe only because of the extremely low attenuation of ELF waves of 1–2 dB per 1000 kilometers.

[12][13] The Russian Navy reportedly operates an ELF transmitter, ZEVS, located northwest of Murmansk on the Kola Peninsula in northern Russia.